For example, the formation of a fine resist pattern on a substrate by a photolithography technique including an exposure step using a KrF excimer laser or an ArF excimer laser as a light source has been known in the manufacture of a semiconductor element. A KrF excimer laser or an ArF excimer laser (incident light) incident to a resist film before the formation of a resist pattern is reflected on a surface of a substrate to generate a standing wave in the resist film. This standing wave has been known to prevent the formation of a resist pattern having a desired shape. In order to suppress the generation of the standing wave, the formation of an anti-reflective coating that absorbs incident light between the resist film and the substrate has been also known. When this anti-reflective coating is provided under the resist film, the anti-reflective coating is required to have a higher dry etching rate than that of the resist film.
Patent Documents 1 to 3 described below describe a resist underlayer film-forming composition or an anti-reflective coating-forming composition that contain a polymer having at least one sulfur atom in a structural unit. When the composition described in each of Patent Documents is used, a resist underlayer film or an anti-reflective coating that has a higher dry etching rate than that of the resist film can be obtained. When a substrate having a concave part on a surface is used in the manufacture of a semiconductor element, a gap-filling material or a planarizing film that allows the concave part of the substrate to be embedded is required. However, all Patent Documents 1 to 3 do not describe or suggest concave part-embedding properties. Further, a reaction of a polymer containing a triazine compound having two thiol groups that is described in Patent Document 2 with a compound having two epoxy groups is unlikely to be controlled during synthesis, and an odor derived from the thiol groups is generated. Therefore, the polymer has a problem in terms of handling.